1. Field of the Invention
The invention relates to a milling cutter and, more particularly, to a ramp, plunge and feed milling cutter for use on high strength, thermal resistant metals such as, for example, titanium alloys, nickel based alloys and cobalt based alloys capable of generating a cavity in the workpiece utilizing one or all of a ramping, plunging or feeding motion.
2. Description of the Background Art
In the past, end mills were used exclusively for motion within a single plane relative to a workpiece. To produce a slot in the workpiece, an initial hole was produced using a drill. An end mill was then introduced into the drilled hole to elongate the hole, thereby producing a slot. This procedure required two separate cutting tools--a drill and an end mill--along with two separate cutting operations.
Some small diameter solid end mills are capable of producing slots within a workpiece. Such end mills have diameters ranging from one-half inch to two inches in diameter and have the capability of machining on their "end" as well as along the side of the end mill.
As illustrated in FIG. 1, an end mill 10 is used to machine a pocket 15 by plunging the end mill 10 into a workpiece 20 a short distance during which a face 25 of the milling cutter actively performs the cutting. An end 30 of the pocket 15 illustrates the distance of the plunge relative to a previous pass illustrated at portion 35. The end mill 10 is then moved in a transverse direction to mill a slot 40 which is the width of the end mill 10 diameter during which a side 45 of the mill 10 actively performs the cutting. Since the slotting operation imposes a very high bending load on the milling cutter, the end mill cannot be plunged deeper than 20% of the mill diameter.
Once the slot 40 is cut the length of the pocket, additional transverse passes of the end mill 10 are made to widen the slot 40 with each pass removing a swath having a width W of approximately one-tenth to one-half the diameter of the end mill. After the slot 40 has been widened to the appropriate dimension of the pocket, the steps are again repeated to plunge a deeper hole, slot the hole and then widen the slot. This procedure is repeated until the desired depth of the pocket is obtained.
Typical end mills used for such an application resemble a twist drill with a flat tip. Milling operations using this type of a tool are the slowest to perform since the full diameter of the milling cutter is being worked to produce a flat floor in the slot.
Indexable inserts are also used on milling cutters for the purpose of providing ramp, plunge and feed capabilities. U.S. Pat. No. 3,811,163 entitled "Plunge Milling Tool" discloses a milling cutter utilizing indexable inserts for performing pocket milling. However, for milling cutters having a two inch diameter or less, such a design is difficult because of space limitations on the milling cutter body. Furthermore, when a milling cutter of this design is made to such a small diameter, the strength of the milling cutter body near the inserts is diminished and may not provide sufficient strength to endure the high forces present in a pocket milling operation.
A milling cutter design is needed having a small diameter suitable for pocket milling operations and furthermore having suitable strength for high metal removal operations.